As mammal neurons do not regenerate if damaged, neurodegenerative diseases such as stroke, Parkinson's disease, or Alzheimer's disease may occur when the neurons are damaged. Accordingly, treatments that can cure diseases due to neuronal death have been actively studied worldwide for a long time, but an adequate treatment has not yet been developed.
Recently, research has been actively carried out to develop a method for treating the neurons damaged by differentiating stem cells, which are pluripotent cells capable of differentiating into various cells, into neurons. As the stem cells can be differentiated into various cells, such method may be fundamental in treating a disease that induces tissue damage. However, as it is not easy to obtain the stem cells or differentiate the stem cells into desired cells, and as the possibility of the stem cells themselves being rejected by patients' immune system can be problematic, the method has not been used universally. However, a cranial nerve disease accompanied by neural damage is considered to be the most appropriate object for the treatment using the stem cells because unlike other tissues, there is little rejection by the immune system in the cranial nervous system tissue, thereby making it possible to expect long-term survival of transplanted cells when the cells are transplanted from outside.
Studies for developing a method for applying the stem cells to treatments of diseases such as stroke, Alzheimer's disease, Parkinson's disease, demyelinating disease, and spinal cord injury are actively under way. For example, International Publication No. WO 2005/003320 discloses a method for inducing the stem cells into neurons, comprising sequentially adding and culturing a basic fibroblast growth factor (bFGF), fibroblast growth factor 8, sonic hedgehog (SHH), and brain-derived neurotrophic factor (BDNF) and ultimately co-culturing with astrocytes. Korean Patent Application No. 10-0495532 discloses a method for differentiating mesenchymal stem cells into neurons by culturing in a culture medium comprising an epidermal growth factor (EGF) and hepatocyte growth factor (HGF) and for proliferating the neurons.
Astrocytes, also known as astroglia, which are a type of neurons, as main supporting cells of the nervous system, are known to play a role in aiding neuronal activities while appropriately eliminating neurotransmitters secreted by neurons and controlling ion concentrations in the brain. Recently, as astrocytes have been revealed to play certain roles, such as in synapse formation of neurons, regulation of synapse number, and synaptic plasticity, and in the onset of degenerative nervous system diseases as well as differentiation of neural stem cells into nerves, more active research has been carried out on whether the astrocytes can be used for treating or improving the neurodegenerative diseases by differentiation.
According to what has been reported so far, a method for differentiating from nerve stem cells into astrocytes via astrocyte progenitor cells (Korean Application Publication No. 10-2014-0071512) and a method of differentiating astrocytes using DMEM/F-12 comprising B-27™ medium supplement (Gibco Life Technologies Corporation, 3175 Staley Road, Grand Island N.Y. 14075, acquired by, and B-27™ medium supplement now distributed by, Thermo Fisher Scientific Inc., Waltham, Mass., USA), bFGF, and heparin (U.S. Pat. No. 6,897,061) are known. However, the astrocytes differentiated by the conventional method include other cells in addition to pure astrocytes, thereby causing a problem in that differentiation efficiency and purity of the astrocytes are low, and this problem has not yet been resolved.